The invention relates to communications systems and especially to communication in a system where a plurality of core networks, possibly incompatible with each other, can be connected to an access network.
Here, a communications system signifies generally a telecommunications system, in which a communication connection may be established by using wired or wireless connection. Wireless communications systems generally signify various kinds of telecommunications systems enabling a personal wireless data transmission when subscribers move within the system. A typical wireless communications system is a Public Land Mobile Network (PLMN). Cordless communications systems also belong to the wireless communications systems.
1st generation mobile systems were analog systems, in which speech or data were transmitted in analog form in the same way as in conventional public switched telephone networks. An example of the 1st generation systems is the Nordic Mobile Telephone (NMT). In 2nd generation mobile systems, such as the Global System for Mobile communication (GSM), speech and data are transmitted in digital form. Digital mobile systems offer, besides conventional speech transmission, also many other services: short messages, telecopy, data transmission, and so on.
At present, 3rd generation mobile systems are being developed, such as Universal Mobile Telecommunications System (UMTS) and Future Public Land Mobile Telecommunication System (FPLMTS), which has later been renamed International Mobile Telecommunication 2000 (IMT-2000). The UMTS is under standardization in the European Telecommunication Standards Institute (ETSI), while the International Telecommunication Union (ITU) standardizes the IMT-2000 system. The basic features of these future systems are very similar. The UMTS, for instance, as all mobile systems, produces wireless data transmission services to mobile users. The system supports roaming, i.e. UMTS users can be reached and they may establish calls anywhere, when they are located within the coverage area of the UMTS.
In present view, the UMTS comprises two or three parts illustrated in FIG. 1: a UMTS Access Network (or UMTS Base Station System, UMTS-BSS) and a Core Network (CN) 2, 3, 4, and 5. Below, the UMTS Access Network is also generally called radio access network. The UMTS Access Network is mainly responsible for matters relating to the radio path, which means that it offers the core network a radio access needed for wireless operation. The core network 2, 3, 4 or 5 is a conventional or future telecommunications network, which is modified to utilize the UMTS Access Network in wireless communication effectively. Telecommunications networks conceivable as suitable core networks are 2nd generation mobile systems, such as Global System for Mobile Communication (GSM), Integrated Services Digital Network (ISDN), Broadband Integrated Services Digital Network (B-ISDN), Packet Data Networks (PDN), Asynchronous Transfer Mode (ATM), and so on.
Accordingly, the UMTS Access Network shall make supporting different core networks possible, also those to be developed in the future. Correspondingly, the UTMS Access Networks should make it possible to connect different radio interfaces to a core network (narrowband, broadband, CDMA, TDMA, and so on). In accordance with the present scenario, the functions of the UMTS Access Network are strictly restricted to the radio access functions. Thus, it mainly contains functions for the control of radio resources (handover, paging) and for the control of bearer service (control of radio network service). More complicated functions, such as registers, registration functions and mobility and location management are located in each core network or in service producers connected to each core network, producing different services for UMTS subscribers.
In accordance with UMTS terminology, the whole UMTS Access Network is called a Generic Radio Access Network (GRAN). The GRAN is divided further into a Radio Access Network (RAN) and an InterWorking Unit (IWU). As a rule, there is a separate IWU between each core network 2 to 5 and the RAN, like the IWUs 1 to 4 in the figure. The purpose of an IWU is a connection between a core network and the RAN. Therefore, the IWU contains the necessary adaptations and other possible interworking functions. The interface between the IWU and the CN is core network specific. This makes it possible to develop the core networks and the RAN regardless of each other. For instance, IWU1 can be connected to the Base Station System (BSS) of the GSM network. Correspondingly, IWU2 can be connected to a local exchange of an ISDN, for instance. In addition, FIG. 1 shows service producers SP1, SP2, SP3, SP4 and SP5, connected to a core network CN2.
In FIG. 1, a radio access network RAN comprises a Transport Network (TN), a Radio Network Controller (RNC) and Base Stations BS1, BS2, BS3 and BS4 and their coverage areas C1, C2, C3 and C4. The figure shows also one subscriber terminal, a mobile station MS, for instance. In the network architecture presented, the base stations are connected to a transport network TN, transporting user data to the IWUs and control signalling to the radio network controller RNC. All the intelligence controlling the GRAN is located in the base stations BS and in the radio network controller RNC. As stated before, this control is typically restricted to control functions associated with radio access as well as to establishing connections through a transport network TN. The TN may be an ATM network, for instance. However, it is to be noted that only one possible implementation of the UMTS access network is presented above.
As was mentioned above, the functions of an access network are restricted to radio access functions. Data transmission over the access network occurs then by using low level protocols corresponding for instance to layers 1 and 2 (physical and data connection layer) of the Open Systems Interconnection (OSI) model. In turn, communication between a wireless mobile station and a core network takes place by using higher level communication protocols of the core network. A wireless mobile station may thus contain several different protocols corresponding to the protocols of those core networks with whom it communicates, and it selects among them each time the one corresponding to the core network to be used. The wireless mobile station may also be arranged to load new communications protocols at its disposal automatically.
A problem with the above system is the routing of Protocol Data Units (PDU) according to a higher level protocol from a wireless mobile station to the correct core network and, respectively, from the core network to the protocol stack which corresponds to the core network of the wireless mobile station. Higher level protocol signifies here for instance protocols corresponding to OSI layer 3 (L3, network layer) and higher protocols. In general, protocol discriminators are used for this, their task being to detect the protocol to which the PDU (or message) in question corresponds. However, it is not sensible or even possible to use protocol discriminators in connection with the UMTS system or the like, for the following reasons: Firstly, the protocol discriminators of different types of core networks (for instance GSM, B-ISDN) are not compatible with each other; their information elements can be of unequal length, for instance. Secondly, if two or more core networks of the same type are connected to the access network, they cannot be distinguished from each other on the basis of the protocol discriminator only, because the protocol discriminators are identical.
As an example of the above problem can be mentioned the use of General Packet Radio Service (GSM/GPRS) systems in connection with some 3G (3rd generation) system. Conventionally, these systems have been used in parallel in such a way that, in each system, a communication connection to a mobile station has been arranged via separate routes such that even the radio path has been separate, on account of which no routing problems as described above have occurred. In the future, the systems (or developed versions of them) will probably be used for instance in connection with the UMTS or a similar system in such a way that at least the radio connection is common, i.e. they use the same radio interface. The systems may also be combined to one unit using one protocol, which unit is then connected to the access network. In cases like this, the above problem with routing protocol data units to the correct system turns up.
The aim of the invention is thus to develop a method and an apparatus implementing the method in such a way that the above problems can be solved. An object of the invention is a method for the control of communication, in which a terminal device communicates with the opposite end via an access network using low level signalling protocols and via a core network connected to the access network, the core network using high level signalling protocols, whereby one or more core networks are connected to the access network, the invention being characterized in that each core network connected to the access network is given a separate identifier and this identifier is used for routing protocol data units of a high level signalling protocol.
The invention is based on that unambiguous network-specific identifiers are created for core networks connected to an access network and the traffic between a mobile station and a core network is routed by means of identifiers.
An advantage of the method of the invention is that the method enables the use of several existing core network protocols in connection with the UMTS or a similar system without any changes being made in the protocol discriminators of the protocols. Further, the invention enables the use of two or more core networks of the same type in the access network. The invention also offers a flexible possibility of updating the system, because core networks of new type can easily be added in parallel with the existing ones. Additionally, the invention makes it easier to combine wireless systems of cellular and other types.
A further object of the invention is a communication system, comprising at least one terminal device, an access network using low level signalling protocols, one or more core networks connected to the access network, the core networks using high level signalling protocols, whereby the system is characterized in that the system is arranged to give each core network connected to the access network a separate identifier and to use this identifier for routing protocol data units of a high level signalling protocol.
Still another object of the invention is a terminal device communicating with an access network, one or more core networks being connected to the access network and the terminal device comprising separate high level signalling protocol stacks for one or more core networks and common low level signalling protocol layers for all core networks, the terminal device being characterized in that the terminal device comprises identifiers corresponding to the core networks, when the terminal device is arranged to use said identifiers for routing received protocol data units of a high level signalling protocol from low level signalling protocol layers to the correct high level signalling protocol stack.
By means of such a system and such a terminal device, the advantages offered by the method of the invention can be achieved in a simple manner.